This invention relates to several useful applications of cross-linked polymers utilizing the inherent memory phenomenon associated with such cross-linked polymeric materials to effect a temporary attachment of a first part to a second part. More particularly, this invention relates to a device and method of using cross-linked polymeric materials wherein a polymer is formed to a first "memory" shape; thereafter the shaped polymer being cross-linked to lock in that first "memory" shape. Next, the shaped polymer is heated and deformed to a second shape; and then cooled to lock in that second shape, the deformed shape effecting attachment or holding to another part. This is followed by a second heating above the polymeric transition temperature which will act to release the held part as the deformed cross-linked polymer reverts back to its first "memory" shape.
The memory characteristics of cross-linked polymeric materials is well known to those skilled in the art. This novel property of cross-linked polymers has been practically utilized in several prior art applications. For example, shrink tubing and the like is one such well known application. In shrink tubing, the cross-linked polymer is expanded and upon heating, reverts back to its original smaller shape. Other examples include U.S. Pat. No. 3,382,121 to Sherlock which discloses a process for preparing a heat recoverable sleeve with a fusible insert held in contact therewith. An extruded or formed longitudinally oriented plastic insert is placed adjacent to a recoverable plastic member and the assembly is thereafter heated to a temperature sufficient to release the stresses in the insert induced by orientation; and to cause the insert to retract in length, and tightly cling to, the recoverable member. In the assembly thus produced, the insert is brought into abutting relationship to the recoverable member.
U.S. Pat. No. 4,343,844 to Thayer et al discloses a shrinkable sleeve of minimal outside diameter made from heat shrinkable material having an elastic memory and adapted to be secured to the end of an electrical cable having one or more electrical conductors and/or tubes extending therefrom to provide a barrier to the flow of gas or vapors therethrough. When the sleeve is in an expanded state, a cavity at one end receives the conductor bundle. The sleeve contains one or more internal channels at the opposite end thereof that are separated from each other by walls that are related to the wall of the remainder of the sleeve.
In U.S. Pat. No. 3,597,372 to Cook, a method is disclosed for making elastomeric products which have the properties of elastic deformation substantially equal to that of true elastomers, and, upon the application of heat, recover to the original cross-linked size. A composition is formed which is then cross-linked by ionizing radiation. The cross-linked article is then heated to a temperature sufficiently high to soften the thermoplastic component. The deformed article is cooled or quenched while still under the external deforming stress. The article is now in the heat-recoverable state, but may be left for an indefinite period of time at room temperature, without danger of its recovering back to its original size and shape.
Evans Pat. No. 3,847,721 discloses an article processed to be heat recoverable in involute fashion to an overlapping, generally cylindrical configuration. The articles are initially heat recoverable to a cross-section "S". The article can be deployed around a substrate to be protected, the arcuate edge portions thereof positioned in interlocking relation, and heat applied to the interlocked edge portion to form a bonded seam.
Finally, U.S. Pat. No. 4,440,712 to Imgram discloses a process for the preparation of shaped articles, particularly tubular shaped polymeric articles, comprising moldable and cross-linkable synthetic plastic material, into a first molded shape, cross-linking the plastic material at a temperature in excess of the crystalline melting point of material, subjecting the cross-linked first shape to a working operation to form a second configuration shape; and subjecting specific areas of the second shape to a heat treatment thereby forming a deformation in the specific area. Other prior art patents of general interest which utilize the memory characteristics of cross-linkable polymeric materials include U.S. Pat. Nos. 2,981,668, 2,086,242, 3,110,553, 3,318,994, 3,370,112, 3,387,065, 3,396,460, 3,420,363, 3,526,863, 3,959,052, and 4,033,534.
It will be appreciated that none of the above described and discussed prior art patents disclose a method of utilizing the inherent "memory" characteristic of cross-linkable polymers for those applications wherein a temporary attachment of a first part to a second part is effected. Such temporary holding of cooperating parts is necessitated in a myriad of industrial, agricultural, construction and safety applications to name but a few. For example in automatic assembly operations, component parts must be temporarily held and oriented so as to be provided to an assembly at a specific time and place. Similarly, in the construction field, fasteners, terminals, rivets and other items be temporarily held in a substrate or bin when being used automatic insertion devices. Fire safety and similar safety applications require parts and assemblies which will be automatically removed to expose sprinkler systems or other devices during fires.
Accordingly, it is an object of the present invention to provide a device and method of using a cross-linkable polymeric material which utilizes the inherent "memory" characteristic thereof to effect temporary holding or attachment between several parts or components in a variety of industrial, agricultural, construction, safety and other applications.
It is still another object of the present invention to provide a process and device for utilizing the "memory" characteristic of cross-linked polymers wherein a polymer "part" is formed to a first shape and cross-linked to hold that first "memory shape"; the cross-linked polymer part being thereafter heated and deformed to temporarily lock on to and hold a second "part", and the polymer part being cooled to lock the second shape therein. Thereafter, when desired, the deformed polymer part is heated above its transition temperature wherein it will revert back to its first memory shape and the held or secured second part will be released. The process of the present invention will thus take advantage of the memory characteristic of cross-linked polymers by holding and thereafter releasing components at specified times and places.
Other objects and advantages of the present invention will be apparent to and understood by those skilled in the art from the following detailed description and drawings.